Can't add AlwaysOn replica

Hello!

I'm trying to add an AlwaysOn replica - db server Guest2 (Windows Server 2012R2 + SQL 2014 Ent.) - to the AlwaysOn group  with a contained DB and getting the following error:

I can't understand should I explicitly set any permissions on an endpoint for this procedure to succeed given that both SQL servers (Guest1 and Guest2) are members of the same domain?

Thank you in advance,

Michael